1. Field of the Invention
This invention relates to foam, a foam-resin composite, i.e., a composite comprising a core or layer derived from said foam and an integral resin layer, and a method of making a foam-resin composite. More particularly, this invention provides a formulation for a rigid, high density urethane modified polyisocyanurate foam which may be combined with a resin layer. The resin is an epoxy resin, a bismaleimide resin, a phenolic resin, or other resin which is cured or post-cured at a temperature of at least 350.degree. F. The foam of this invention may be used in a variety of situations where dimensional stability at elevated temperatures, machinability, and light weight are factors of concern. Also, this foam may be used in a variety of manufacturing techniques to make composite or resin finished products. The foam-resin composite of this invention may be used in a variety of situations where high strength and light weight are factors of concern.
2. Description of the Related Art
For a variety of reasons and in a variety of products, it is often desired to combine a rigid foam with a layer of a high strength material, such as a resin, to form a composite having high strength yet low weight. A first type of foam-resin application is the fabrication of foam core panels or laminates for aerospace, aircraft, automobile, boat, surfboard, ski, skateboard, etc. In this application, the composite is used to form a strong, yet lightweight, structure where the foam provides functions such as structural reinforcement, or heat or noise insulation.
A second application of foam-resin composites is the construction of molds, models and prototypes. Here, a foam-resin composite may be desired because a foam may be shaped to the desired form and a resin may be applied to a surface having significant curvature or other non-uniformities.
While the combination of various foams and various resins to form foam-resin composites is generally known, foam-resin composites having a resin layer of epoxy resin, bismaleimide resin or phenolic resin and having cure or post-cure temperatures of at least 350.degree. F. have uniformly been unsuccessful due to the high temperatures and/or pressures required to cure these resins and/or foam incompatibility with these resins. Known foams are unsuitable when using these resins because of dimensional instability at elevated temperatures, i.e., the foam volume shrinks significantly or otherwise does not hold the desired shape, lack of tensile strength, and low compressive strength, i.e., the foam will not maintain the desired shape in high temperature, high pressure cure/post-cure conditions.
There exists a need for a foam-resin composite, wherein the resin layer is formed of an epoxy resin, a bismaleimide resin, a phenolic resin, or other resins requiring cure or post-cure temperatures of at least 350.degree. F., and the foam is formulated so as to maintain dimensional stability, provide suitable compressive and tensile strength, and avoid thermal or chemical degradation with these resins.
In addition the need exists to develop a foam which does not contribute to ozone depletion. Many commercial foams are made using chlorofluorocarbons as blowing agents in the production of the foam. Chlorofluorocarbons, including hydrogenated chlorofluorocarbons, are known to deplete the ozone in the earth's atmosphere. With these prior art foams, the chlorofluorocarbons are trapped within the closed cells when the rigid foam is produced. Thus, the chlorofluorocarbons produce a detrimental environmental effect both when the foam is produced and later, when it degrades and the closed cells release the entrapped chlorofluorocarbons, such as, for example in a landfill. Thus, there exists a need to manufacture foam in such a fashion as to avoid ozone depletion.